The satellite signals from Global Navigation Satellite Systems (GNSS), such as Global Positioning System (GPS), GLONASS, Galileo, and COMPASS are currently available for mobile devices, also referred to as GNSS-enabled devices, itself. The GNSS signals include ranging signals, used to measure the pseudo-range to the satellite, and navigation messages. The navigation message consists of three major components. The first part contains the GNSS date and time, plus the satellite's status and an indication of its health. The second part contains orbital information and allows the GNSS-enabled device to calculate the position of the satellite. The third part, called the almanac, contains information and status concerning all the satellites; their locations and pseudorandom noise numbers. The GNSS-enabled device may receive signals from a sufficient number of GNSS satellites, extract the necessary navigation message from the signals, and then use the navigation message in conjunction with ranging signals to provide position, velocity, and timing services, and the related applications. An important performance index of the satellite based positioning systems is the time-to-first-fix (TTFF). The TTFF is the time required for the GNSS-enabled device to acquire the satellite signals and calculates its position under a variety of conditions. For best user experience however, it is desirable that TTFF be minimized.
Ephemeris transmitted from a satellite is known as broadcast ephemeris. The broadcast ephemeris contains the orbital information of the satellite and the period of validity of this orbital information. In general, the broadcast ephemeris is only valid for a four hour period. The broadcast ephemeris describe a Keplerian-like set of orbital elements with additional corrections that then allow the satellite's position to be calculated in an Earth-centered-Earth-fixed (ECEF) Cartesian coordinates at any time during the period of validity of the broadcast ephemeris. When the validity period for the previously obtained broadcast ephemeris has expired, the GNSS-enabled device is required to retrieve current broadcast ephemeris as the GNSS-enabled device needs to calculate the satellite state. Typically, the current broadcast ephemeris can be obtained as direct broadcast from a GNSS satellite. Alternatively, satellite ephemeris may be received from a server in real time. Real time deliver real broadcast ephemeris that is being observed concurrently by a neighboring receiver's station, or by a network of reference receiver's station that relay to a data center all the current broadcast ephemeris received from every satellite in view at each reference receiver's station. Further, the GNSS-enabled device is in a position from which it can obtain the broadcast ephemeris from a GNSS satellite and properly demodulate the signal, the process of receiving and demodulating increases substantially to the processing time. The additional processing time certainly increases the TTFF while increasing the power consumption of the GNSS-enabled device.
Accordingly, there is a need in the art for the GNSS-enabled device that determines position, velocity, and timing services by making the ephemeris for future times available to the device.